Motor control damping circuit

ABSTRACT

The circuit controlling the motor which actuates a control potentiometer or the like is made up of operational amplifiers and resistors connected so that, at stall, the feedback loop is not effective and the feedback loop is effective only when the motor is turning, which provides the desired rate feedback for servo damping.

United States Patent Inventor Robert L. Charlton 1 Earlysville, Va.Appl. No. 64,543 Filed Aug. 14, 1970 Patented Nov. 2, 197 l AssigneeTeledyne, Inc.

Los Angeles, Calif.

MOTOR CONTROL DAMPING CIRCUIT Primary Examiner-T. E. Lynch 7 Claims 5Drawing Figs ABSTRACT: The circuit controlling the motor which actuatesU.S. Cl 318/616, a control potentiometer or the like is made up ofoperational 318/663 amplifiers and resistors connected so that, atstall, the feed- Int. Cl G051) 5/01 back loop is not effective and thefeedback loop is effective Field of Search 318/616, only when the motoris turning, which provides the desired 621, 663 rate feedback for servodamping.

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M07019 RHTE VOLT/96E INVENTOR M x Wm MOTOR CONTROL DAMPING CIRCUIT Inprior methods for obtaining rate feedback for controlling motors drivingpotentiometer wipers or other means the number of electrical componentsrequired has been greater than in my circuits, and, in addition, myimproved rate feedback system provides more reliable and smoothercontrol of the potentiometer drive motor.

It is an object to provide a rate feedback circuit or system for closelycontrolling motors which drive potentiometer wipers or for otherapplications.

Another object is to provide suitable damping for motors drivingpotentiometer wipers or the equivalent. Of course the potentiometerwiper could be stationary and the winding or resistor element of thepotentiometer could be shifted.

A further object is to provide a reliable motor-damping system orcircuit which is relatively simple.

Other objects will be evident in the following description.

In the drawings;

FIG. 1 illustrates my improved motor drive with rate damping.

FIG. 2 shows a fragmentary portion of the circuit, including the motorand connected resistor.

FIG. 3 shows fragmentary circuit including the components of FIG. 2 butproducing a different potential across the motor.

FIG. 4 shows a prior circuit arrangement showing the greater number ofelectrical components necessary in order to approximate the resultsachieved by applicants simple partial circuits of FIGS. 2 and 3.

FIG. 5 is a circuit illustrating particularly the novel features of myinvention.

In FIG. 1, showing my improved servoamplifier circuit, voltage e is thefollowup voltage and voltage e, is the input voltage. Amplifier A, sumsvoltage e, and e and voltage e, is the amplified servo error. Thefollowup potentiometer I is mechanically connected to the DC motor M, insuch manner that the amplified error voltage e, causes the motor torotate followup potentiometer I to reduce the servo error. Rotation ofthe motor feeds the back E.M.F. e, of the motor to the summing junctionE, of amplifier A for rate damping.

The rate feedback circuit is believed to be novel, as explained below.Referring to FIG. 2, by making the resistor R exactly equal to thearmature resistance of the motor, and dur ing the interval before themotor starts to turn, the voltage e is precisely equal to the summingjunction voltage 3,, or one-half of voltage V supplied to differentialamplifier A,, as shown in FIG. 1.

Thus, at stall, the feedback loop including resistor R is not effective.This is another way of saying that this feedback loop is effective onlywhen the motor is turning, which provides the desired rate feedback forservo damping. At stall the voltage E, is half the supply voltage. Thisis an important condition.

Operational amplifier A, provides voltage gain for reducing the servodeadband and operational amplifier A exactly inverts the voltage e, sothat the rate feedback bridge including resistor R, and Motor M,functions properly. This circuit is superior to the conventionalcircuitry for obtainingrate feedback since only one series component isrequired to obtain the rate feedback.

My new circuit for obtaining rate feedback is shown in FIG. 3 and theold, conventional circuit for this purpose is shown in FIG. 4. It isobvious that the conventional circuitry is considerably more complicatedthan my new, improved circuit illustrated in FIG. 3. Temperaturestability can be obtained in my circuit by making the resistance ofelement R equal to the armature resistance of motor M,. At stall e isequal to e,,.

The values of components shown in the circuits are not to be consideredas exclusive but are indicated as typical values. The inventioncontemplates two important considerations, however. First, theresistance of resistor R should be equal to the resistance of thearmature of motor M, and, secondly, the ratio of resistance of element Rto that of element R should be I. The resistance of element R, can bechosen to control the damping ratio.

The circuit shown in FIG. 5 illustrates clearly general principlesunderlying my invention and the related analysis below is provided toclarify any uncertainties regarding the principles of operation of thecircuitry.

Under stall conditions, the static voltage gain E /e is given by theequation where "a" is equal to the proportional resistance betweenpotentiometer wiper or slide W and point Z as compared to the totalpotentiometer resistance RI. and R." represents the armature resistanceof the motor. For proper circuit alignment the term should equal 1. Thusthe circuit gain is simply the ratio R,,/R, which means that thefeedback loop including resistor R is only active for rate feedback.

When a =l, R =R and R,r- (on open circuit). Then which is the simplifiedcircuit equation of FIG. I.

When components are chosen so that the circuit gain E /e is determinedby resistors Rn/R It may be desirable to increase this gain by addingpositive feedback which would cause the motor to dither and break thestatic friction of the gear train. For example if the denominator ofequation l is made less than I by component selection the gain will beincreased proportionally, resulting in a lowlevel motor oscillationwhich serves to reduce the static gear train friction.

Referring to the circuit of FIG. 5, by adjusting potentiome ter R theservo deadband can be selected. This circuit represents essentially thenovel features of my invention. The voltage e, at the summing junctionshown is comparable to that atjunction e of FIG. 1. If, in the circuitshown in FIG. 5, the resistance of element R is equal to the resistanceof the motor armature R,,,. and if the resistance of element R is equalto the resistance of element R then the potentiometer resistor R can beeliminated and conductor W, can be connected directly to junction I4. Ifthe circuit of FIG. 5 is employed as shown the resistance of element Rshould be less than the motor armature resistance. With my improvedcircuit only one takeoff at the motor feeds operational amplifier A andthe voltage at e, is always equal to half the supply voltage V. Thevoltage at e, stays steady at V/2 whereas the equivalent voltage in FIG.4 does not.

The amplifiers A and A connected as shown, are preferably integratedcircuit operational amplifiers.

What I claim is:

1. In a motor control circuit for providing rate damping of said motor,a first operational amplifier and a second operational amplifierconnected in series therewith, a series connected first resistor in theinput of said first amplifier and a second resistor connected inparallel with said first amplifier, a third resistor connecting theoutput of said first amplifier with the input of said second amplifier,a fourth resistor connected in parallel with said second operationalamplifier, the ratio of the resistance of said fourth resistor to theresistance of said third resistor being one, a fifth resistor connectedwith the output of said first amplifier and in series with the armatureof said motor which is connected to the output of said second amplifier,and a sixth resistor electrically connecting the input of said firstoperational amplifier with the junction of said motor armature and saidfifth resistor.

2. The motor control circuit as described in claim 1, the

ratio of the resistance of said fifth resistor to the resistance of saidarmature being one.

3. The motor control circuit as described in claim 1, and including avariable resistance connecting said sixth resistor with said motorarmature.

4. The motor control circuit as described in claim 1, and including apotentiometer connected in parallel with said motor armature andconnected with said sixth resistor.

5. The motor control circuit as described in claim 1, the ratio of theresistance of said second resistor to the resistance of said firstresistor being, optionally, from one to l ,000.

6. The motor control circuit as described in claim 3, the resistance ofsaid fifth resistor being less than the resistance of said motorarmature.

1. In a motor control circuit for proViding rate damping of said motor,a first operational amplifier and a second operational amplifierconnected in series therewith, a series connected first resistor in theinput of said first amplifier and a second resistor connected inparallel with said first amplifier, a third resistor connecting theoutput of said first amplifier with the input of said second amplifier,a fourth resistor connected in parallel with said second operationalamplifier, the ratio of the resistance of said fourth resistor to theresistance of said third resistor being one, a fifth resistor connectedwith the output of said first amplifier and in series with the armatureof said motor which is connected to the output of said second amplifier,and a sixth resistor electrically connecting the input of said firstoperational amplifier with the junction of said motor armature and saidfifth resistor.
 2. The motor control circuit as described in claim 1,the ratio of the resistance of said fifth resistor to the resistance ofsaid armature being one.
 3. The motor control circuit as described inclaim 1, and including a variable resistance connecting said sixthresistor with said motor armature.
 4. The motor control circuit asdescribed in claim 1, and including a potentiometer connected inparallel with said motor armature and connected with said sixthresistor.
 5. The motor control circuit as described in claim 1, theratio of the resistance of said second resistor to the resistance ofsaid first resistor being, optionally, from one to 1,000.
 6. The motorcontrol circuit as described in claim 3, the resistance of said fifthresistor being less than the resistance of said motor armature.